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Tuesday December 3, 2013 Agenda: O Homework Check O Discussion: Why Cells Divide, Chromosomes & Preparing for Mitosis: -------------Warm Up------------------------------------------------

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Presentation on theme: "Tuesday December 3, 2013 Agenda: O Homework Check O Discussion: Why Cells Divide, Chromosomes & Preparing for Mitosis: -------------Warm Up------------------------------------------------"— Presentation transcript:

1 Tuesday December 3, 2013 Agenda: O Homework Check O Discussion: Why Cells Divide, Chromosomes & Preparing for Mitosis: -------------Warm Up------------------------------------------------ 1. What is DNA replication and what is its goal? ----------HW: ------------ O Re-read outlines on CH9: Cell cycle, Chromosomes and Mitosis. Test on DNA, Cell Cycle Gene Expression, Replication, Mitosis, & maybe Mutations 12/11-12/12 Without looking at your notes, what is… a. b. c. d. e. f. g. h. d e c b g f h a g

2 Homework Check

3 Mitosis Objective Students will understand the process of The Cell cycle. The students will also be able to demonstrate the process of Mitosis and how the purpose aides life.

4 How do we, as organisms, get to be the size we are when we finally finish growing from such simple origins? There are two solutions. One way is for that one fertilized cell to keep getting larger and larger. But that would result in a gigantic blob and you know cells are very small. Upon conception, a sperm fertilizes an egg. From this point, the DNA from dad and mom are joined to give a new organism all the DNA it needs to live. But the size of a fertilized egg is microscopic. The Two Possible Outcomes

5 Amoeba Norris OR Chuck Norris Unicellular Multi-celled

6 Option Two The second option, the one that really happens, is we grow as a result of the number of our cells growing. The number of cells grow from the existing cells that are already there. The existing cells split in half, giving birth to 2 identical versions of itself. The growing number of cells each survive independently but work together to give rise to complex multicellular organisms, like humans. This process of cell division is a vital part of development, of healing, of life.

7 DNA Packaging: Objectives List 3 reasons why cells divide. Describe three levels of structure in the DNA packaging in the nucleus. Explain what are daughter cells and why they are identical to the parent cells. Describe how cells (both prokaryotic and eukaryotic) prepare for division. Vocabulary: Gene Chromosome Chromatin Histone Nucleosome Chromatid Centromere

8 Cells don’t last forever Remember, cells don’t last forever… they have a life span like we do as organisms. You’ve learned in G1 cells primarily grow, performing transcription and translation. You’ve also learned that in S phase DNA is duplicated. We will now focus on G2, when cells finish growing and prepare for division.

9 What do these things have in common? Human Growth Growth of plant Wound healing

10 What is Cell Reproduction? As the body of a multicellular organism grows larger, its cells do not just grow large too. Instead, the body grows by increasing the number of the same size cells. –An adult human can produce up to around 2 trillion cells per day! This is known as cellular reproduction. Or more commonly, mitosis.

11 Why Cells Reproduce There are three main reasons cells divide: 1. To help tissues and organs grow. –We continuously add cells as we grow to get bigger. 2. To replace cells. –As old cells die or cells get damaged new cells take their place in order to maintain health. –As the cell ages, it continues to grow. When it gets too big it need to be replaced to limit cell size. 3. To repair broken cells. –When cells get damaged due to trauma they need to be replaced.

12 Why Cells Reproduce… Growth & Development Aging is inevitable. But a cell only last so long. –Some last days, some decades As one cell dies others replace it.

13 Why Cells Reproduce… Replacing Old Cells What constitutes an old cell? A cell is old when it gets too big. As a cell ages it grows by producing more proteins & more organelle. As a cell grows its surface-area-to-volume ratio decreases. Remember, cells are small because it is more efficient to be small than big.

14 Think of a Cell as a Protein Factory Amino acids, sugars, lipids PROTEINS WASTE

15 Why Cells Reproduce… Replacing Broken Cells = Healing Wounds What constitutes BROKEN CELLS? Cells damaged from: –Trauma –Burns –Cancer


17 Recap What are three reasons cells reproduce? –To allow an organism to grow. –To replace old cells (that get too big). –To allow an organism to replace damage.

18 Why Cells Reproduce, Making New Cells This all ties in to one major theme. Other than repairing broken cells or for growing… Cells divide when they reach a certain size, because larger cells are more difficult to maintain. Small cells are MUCH more efficient than large cells.

19 Facts of Cell Division When a cell divides it forms “daughter” cells –Each newborn “daughter” cell is smaller than the parent and has a higher surface area–to-volume ratio than its parent does. –It inherits half of the parent cell’s organelle necessary for life (mitochondria, ER, Golgi, Etc.) –Also, each new daughter cell gets an entire, exact copy of the parent cell’s DNA. (produced in replication) –They are, in essence, identical twins & clones of the parent.

20 What Must Happen First…DNA Packaging You now know why a cell divides. –It’s to replace old or damaged cells,… –To grow,… –Or when the cell reaches a certain size. Now, before you learn about the process of mitosis, you need to learn about the structure of chromosomes and how DNA is prepared for efficient separation into two daughter cells.

21 You know that DNA carries Genetic Information. The genetic information is arranged on large molecules of DNA organized into hereditary units called genes. –Recall: A gene is a unit of heredity that consists of a segment of nucleic acid that codes for a functional unit of RNA or protein. Chromosomes GENE

22 Chromosomes This form is called chromatin. Chromatin = a complex of DNA & proteins called In this form, the genetic information is easily accessed to make proteins. But before a cell can divide, the DNA must be condensed, or wound up into a smaller, more organized unit…into chromosomes. WHY? = so that DNA doesn’t get messed up during division. Eukaryotic Chromosomes During most of a cell’s life, its chromosomes exist in the nucleus like spaghetti noodles in a bowl.

23 Chromosomes Ultimately, before a cell can divide its genes in DNA it’s organized and packaged (condensed) into structures called chromosomes. –Depending on the organism, chromosomes are linear structures (eukaryote) or a circular structure (prokaryote) that is made up of DNA and proteins.


25 1 st level of Organization. Eukaryotic Chromosomes The first level of packaging is done by a class of proteins called histones. A complex of eight histones come together to form a disc-shaped core. –A type eukaryotic protein found in the chromosome The long DNA molecule is wound around a series of histone cores in a regular manner to make what is called a nucleosome. –A eukaryotic structural unit of chromatin of DNA wound around histones Under an electron microscope, this level of packaging resembles beads on a string.


27 2 nd Level of Organization The 2 nd Level The string of nucleosomes line up in a spiral to form a cord that is 30 nm in diameter.

28 3 rd Level of Organization Eukaryotic Chromosomes The 30-nm nucleosome cord forms visible chromosomes around protein scaffolding. These looped domains then coil into the final, most highly condensed form of the chromosome. Many dense loops of chromatin form the rod-shaped structures that can be seen in regular light microscopes. –After the several condensing steps, the chromatin is dense enough to be seen by the eye in one of our microscopes


30 Chromosomes Eukaryotic Chromosomes Chromosomes are drawn as “X”s It’s actually 2 identical chromosomes that have been replicated joined in the center. Each of the two thick strands of a fully condensed, duplicated chromosome are called a chromatid. –Each chromatid is made of a single, long molecule of DNA.. CHROMATID #1 CHROMATID #2

31 Chromosomes Eukaryotic Chromosomes Identical pairs of chromatids, called sister chromatids, are held together at a region called the centromere. –The region of the chromosome that holds the two sister chromatids together during mitosis Why do the sister chromatids need to be identical? During cell division, the sister chromatids are separated at the centromere, and one ends up in each daughter cell. They need to be identical so the daughter cells will have the exact same genes and do the exact same things.

32 Summary All new cells are produced by the division of preexisting cells. –This idea is a cornerstone of CELL THEORY G1 = (Transcription and Translation) Cells “Live”. They make proteins & the directions for those proteins are contained in the genes of DNA. S = (Replication) DNA and all the genes are duplicated so there exists two copies of all the genetic information. G2 = Organelle is duplicated and DNA is condensed into chromosomes. Mitosis and Cytokinesis = (Next Topic) Division of the nucleus and cytoplasm. The process of cell division involves more than cutting a cell into two pieces. Each new cell must have all of the equipment (organelle… mitochondria, etc) needed to stay alive.

33 A Chromosome Under Electron Microscopy E 1 Sister Chromatid A B C D Where are CHROMATIDS? Pick a letter(s). 1 Chromosome CONCEPT CHECK

34 A Chromosome Under Electron Microscopy The place where 2 sister chromatids are joined A B C D Where is the CENTROMERE? E CONCEPT CHECK

35 A Chromosome Under Electron Microscopy This is the stuff that all DNA in chromosome form is made of. A B C D What is CHROMATIN? E CONCEPT CHECK

36 A Chromosome Under Electron Microscopy Chromosomes are the most condensed and organized form of DNA A B C D What is the CHROMOSOME? E CONCEPT CHECK

37 Concept Check: Talk with shoulder partner and determine which letter corresponds to the graphic. Word Bank: Sister chromatid DNA Nucleus 30nm-cord DNA around protein scaffold Centromere Chromosome Nucleosome A C B D E F H A C B D E F G G H

38 Summary: Answer these questions. Why do Cells Divide? What happens to DNA before a cell can divide? What helps DNA condense? What is special about daughter cell and parent cell DNA?

39 Summary of Chromosome Packaging

40 Application Tissue Regeneration Pinky Nail Regrowth

41 Prokaryotic Chromosomes Prokaryotic Chromosome Organization Prokaryotes are much simpler than eukaryotes. A prokaryotic cell has a single circular molecule of DNA. –Normally, it’s connected on both ends, in a loop This loop of DNA contains thousands of genes. A prokaryotic chromosome is condensed through repeated twisting or winding, like a rubber band twisted upon itself many times. This is called supercoiling.

42 Preparing for Cell Division Prokaryotes Once supercoiled, the bacterial DNA is protected In order for bacteria to divide the DNA must unwind, get copied and attached to the inner cell membrane Once attached the bacteria is ready to divide.

43 Preparing for Cell Division Prokaryotes Division in Prokaryotes is much more basic. The process of Prokaryotic cell division is called binary fission. It happens in three steps. 1.The cytoplasm is divided when a new cell membrane forms between the two DNA copies. 2.The cell grows until it nearly doubles in size. 3.The cell is then constricted in the middle, like a long balloon being squeezed near the center. Eventually the dividing prokaryote is pinched into two independent daughter cells, each of which has its own circular DNA molecule exactly the same as the parent.

44 Binary Fission

45 Preparing for Cell Division, continued Eukaryotes The reproduction eukaryotic cells is more complex than that of prokaryotic cells. Reasons: Eukaryotic cells have many organelles. In order to form two living cells, each daughter cell must contain enough of each organelle to carry out its functions. The daughter cells being smaller only need a few organelle at first but as it grows, makes more of each organelle. The DNA within the nucleus must also be copied, sorted, and separated. Eventually, the daughter cells become mature cells, exactly like their parent cells, equipped with the same amount of DNA & organelle.

46 Comparing Cell Division in Prokaryotes and Eukaryotes Because of its complexity, eukaryotic cell division takes roughly 24 hours. Prokaryotic cell division requires only 20 minutes. Being infected by one cell can result in our bodies being overrun by millions of bacteria in less than a day.

47 Summary Reflection In your notes, list 3 things you have learned today. List at least one thing you are unsure about and need to study more. Next up: You will use this information to better understand mitosis!

48 Summary Because larger cells are more difficult to maintain, cells divide when they grow to a certain size. Many proteins help package eukaryotic DNA into highly condensed chromosome structures. All newly-formed cells require DNA, so before a cell divides, a copy of its DNA is made for each daughter cell.

49 The Organization of DNA Take a piece of string and stretch it out. This is how long all the DNA in just one cell would be if it were stretched out… 2 meters. It takes great organization to get this much DNA to fit into each of the 100 trillion cells you have. Try fitting two “chromosomes” into your “nucleus”. Try once just shoving it in then wrap the chromosome around a paperclip. Which way is more organized? This organization is called condensation. What does the word condensed mean?


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